Sodium lactate infusions result in panic attacks in more panic disorder patients than control subjects. This finding has been confirmed by many laboratories, but it has been difficult to establish consistent biological differences between panic patients and controls. We have obtained preliminary data that lactate panic anxiety increases linearly with increasing lactate levels and oxygen consumption. This suggests there is an abnormality of aerobic metabolism in panic disorder patients. However, lactate panic anxiety also increases linearly with increases in minute ventilation and heart rate, and the rate of this increase is greater in patients than controls, a finding consistent with the hypothesis that panic disorder patients are psychologically hypersensitive to the physical effects of lactate. Atropine does not increase lactate levels or oxygen consumption but does increase minute ventilation and heart rate, and produces many of the subjective effects of lactate as well as symptoms associated with panic anxiety. In the study proposed here, we will compare the effects of lactate and atropine in panic disorder patients and control subjects. If panic disorder patients have panic attacks during lactate but not atropine infusions, it is unlikely that lactate panic anxiety is solely the result of a psychological hypersensitivity to the physical effects of lactate. If the attacks are associated with an increase in oxygen consumption, they may be a result of the metabolic effects of lactate. If lactate panic anxiety is associated with greater oxygen consumption in panic disorder patients than controls, panic disorder patients may have an abnormality of aerobic metabolism. However, it is possible that panic disorder patients will experience both lactate and atropine induced panic attacks. This would provide evidence that panic disorder patients are psychologically hypersensitive to the physical effects of lactate. In either case, this study should help define the relationships between the physiological and psychological changes that occur during lactate induced panic anxiety.